Thermal conductivity of metals mainly depends on

 

Q601–Q700

601. The Fermi level in n-type semiconductor is
A) Near conduction band
B) Near valence band
C) Mid-gap
D) Zero
Ans: A

602. Drift current in semiconductors depends on
A) Carrier mobility, concentration, and electric field
B) Only electric field
C) Temperature only
D) Material density
Ans: A

603. Diffusion current in semiconductors occurs due to
A) Concentration gradient
B) Electric field
C) Magnetic field
D) Temperature
Ans: A

604. The electron mobility in silicon at 300 K is approximately
A) 1350 cm²/V·s
B) 450 cm²/V·s
C) 1000 cm²/V·s
D) 1500 cm²/V·s
Ans: A

605. Hole mobility in silicon at 300 K is approximately
A) 450 cm²/V·s
B) 1350 cm²/V·s
C) 800 cm²/V·s
D) 2000 cm²/V·s
Ans: A

606. In a semiconductor, resistivity decreases with
A) Increase in temperature
B) Decrease in temperature
C) Constant temperature
D) Pressure
Ans: A

607. The intrinsic carrier concentration of silicon at 300 K is about
A) 1.5×10¹⁰ cm⁻³
B) 10¹² cm⁻³
C) 10¹⁴ cm⁻³
D) 10⁸ cm⁻³
Ans: A

608. The band gap of GaAs is approximately
A) 1.43 eV
B) 0.72 eV
C) 1.1 eV
D) 2 eV
Ans: A

609. Doping increases conductivity of semiconductors by
A) Introducing carriers
B) Decreasing mobility
C) Increasing resistivity
D) Reducing lattice defects
Ans: A

610. Donor impurities in silicon create
A) N-type semiconductor
B) P-type semiconductor
C) Insulator
D) Conductor
Ans: A

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611. Acceptor impurities in silicon create
A) P-type semiconductor
B) N-type semiconductor
C) Insulator
D) Conductor
Ans: A

612. The intrinsic semiconductor at 0 K behaves as
A) Insulator
B) Conductor
C) Semiconductor
D) Superconductor
Ans: A

613. Extrinsic semiconductors are made by
A) Doping intrinsic semiconductors
B) Heating metals
C) Cooling metals
D) Applying voltage
Ans: A

614. Hall effect can determine
A) Type of semiconductor
B) Carrier concentration
C) Magnetic field
D) All of these
Ans: D

615. Semiconductor diodes function due to
A) PN junction
B) Magnetic effect
C) Mechanical strain
D) Piezoelectricity
Ans: A

616. Zener diode is used for
A) Voltage regulation
B) Rectification
C) Amplification
D) Oscillation
Ans: A

617. Forward bias in a PN junction causes
A) Current flow
B) Reverse current
C) No current
D) Breakdown
Ans: A

618. Reverse bias in a PN junction causes
A) Very small leakage current
B) Large forward current
C) Oscillation
D) Heating
Ans: A

619. The resistivity of silicon decreases with
A) Increase in temperature
B) Decrease in temperature
C) Constant temperature
D) None
Ans: A

620. Band gap of diamond is approximately
A) 5.5 eV
B) 1.1 eV
C) 0.72 eV
D) 3.4 eV
Ans: A

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621. Silicon carbide is
A) Wide bandgap semiconductor
B) Narrow bandgap semiconductor
C) Metal
D) Insulator
Ans: A

622. Piezoelectric materials generate voltage when subjected to
A) Mechanical stress
B) Magnetic field
C) Heat
D) Electric current
Ans: A

623. The unit of magnetic susceptibility is
A) Dimensionless
B) H/m
C) Tesla
D) A/m
Ans: A

624. Magnetic saturation occurs when
A) All magnetic domains are aligned
B) Material is heated
C) Voltage applied
D) Material cooled
Ans: A

625. Retentivity is the ability of a material to
A) Retain magnetization after removal of field
B) Resist current
C) Store electric energy
D) Conduct electrons
Ans: A

626. Coercivity is
A) Reverse field required to reduce magnetization to zero
B) Magnetic flux density
C) Permeability
D) Electric field strength
Ans: A

627. Soft magnetic materials have
A) Low coercivity
B) High coercivity
C) Zero permeability
D) High resistivity
Ans: A

628. Hard magnetic materials have
A) High coercivity
B) Low coercivity
C) High conductivity
D) Low permeability
Ans: A

629. Eddy currents are minimized in transformer cores by
A) Laminating the core
B) Using solid cores
C) Increasing voltage
D) Cooling
Ans: A

630. Hysteresis loss depends on
A) Area of B-H loop
B) Material density
C) Resistivity
D) Conductivity
Ans: A

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631. Ferrites are
A) Ceramic magnetic materials
B) Metallic conductors
C) Semiconductors
D) Insulators only
Ans: A

632. Transformer cores use silicon steel to
A) Reduce hysteresis loss
B) Increase resistivity
C) Increase conductivity
D) Reduce permeability
Ans: A

633. The dielectric constant of vacuum is
A) 1
B) 2
C) 3
D) 0
Ans: A

634. Dielectric materials store energy in the form of
A) Electric field
B) Magnetic field
C) Thermal energy
D) Mechanical energy
Ans: A

635. The dielectric strength of air is approximately
A) 30 kV/cm
B) 10 kV/cm
C) 50 kV/cm
D) 100 kV/cm
Ans: A

636. Mica is used in capacitors due to
A) High dielectric strength
B) High conductivity
C) Low resistivity
D) Ferromagnetic properties
Ans: A

637. Quartz is used in oscillators because of
A) Piezoelectric property
B) Magnetic property
C) Conductivity
D) Thermal property
Ans: A

638. Electrical resistivity of copper at 20°C is approximately
A) 1.7×10⁻⁸ Ω·m
B) 2.7×10⁻⁸ Ω·m
C) 10⁻⁶ Ω·m
D) 10⁻⁵ Ω·m
Ans: A

639. Electrical resistivity of aluminum at 20°C is
A) 2.7×10⁻⁸ Ω·m
B) 1.7×10⁻⁸ Ω·m
C) 10⁻⁶ Ω·m
D) 10⁻⁵ Ω·m
Ans: A

640. The Hall coefficient of a semiconductor is
A) Inversely proportional to carrier concentration
B) Proportional to resistivity
C) Independent of carrier type
D) None
Ans: A

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641. The coercivity of soft iron is approximately
A) 10–100 A/m
B) 1000 A/m
C) 5000 A/m
D) 10000 A/m
Ans: A

642. Hysteresis loss is minimized by using
A) Soft magnetic materials
B) Hard magnetic materials
C) High conductivity materials
D) Non-magnetic materials
Ans: A

643. Hard ferrites are used for
A) Permanent magnets
B) Transformer cores
C) Electromagnets
D) Conductors
Ans: A

644. Soft ferrites are used for
A) High frequency transformer cores
B) Permanent magnets
C) Motors
D) Conductors
Ans: A

645. Magnetic flux density B = μ H. Here μ is
A) Permeability
B) Conductivity
C) Resistivity
D) Retentivity
Ans: A

646. Saturation magnetization is reached when
A) All domains align
B) Material is cooled
C) Magnetic field removed
D) None
Ans: A

647. Thermal conductivity of metals mainly depends on
A) Free electrons
B) Phonons
C) Lattice vibrations
D) Ions
Ans: A

648. Conductivity of metals decreases with
A) Increase in temperature
B) Decrease in temperature
C) Constant temperature
D) Pressure
Ans: A

649. The temperature coefficient of resistance for semiconductors is
A) Negative
B) Positive
C) Zero
D) Variable
Ans: A

650. The intrinsic carrier concentration of germanium at 300 K is approximately
A) 2.5×10¹³ cm⁻³
B) 1×10¹⁰ cm⁻³
C) 10¹² cm⁻³
D) 10⁸ cm⁻³
Ans: A